Optical head and optical recording apparatus

ABSTRACT

An optical head having: a graded index lens which receives incident light radiated from a linear optical guide at one end surface of the graded index lens and transmits the incident light from the other end surface of the graded index lens, the graded index lens is adapted to form a light spot at a position that is away from the other end surface from which the incident light is transmitted; a light path deflection section which deflects light transmitted from the graded index lens, the light path deflection section is arranged between the other end surface from which the incident light is transmitted and the position where the light spot is formed; and a slider which floats on a recording medium while moving relative to the recording medium, wherein at least the graded index lens and the light path deflection section are installed on the slider.

CROSS REFERENCE TO RELATED APPLICATION

The present application is based on Japanese Patent Application No.2006-181127 filed in Japan on Jun. 30, 2006, the entire contents ofwhich are incorporated herein by reference.

TECHNICAL FIELD

This invention relates to an optical head and optical recordingapparatus.

BACKGROUND OF THE INVENTION

In a magnetic recording mode, a magnetic bit is affected greatly byenvironment such as ambient temperature when a recording density becomeshigh. Because of this, a recording medium having coercive force isrequired. But when using such recording medium, strong magnetic field isrequired for recording. Higher limit of a magnetic filed generated by arecording head is determined by a saturation magnetic flux density. Butthe value of the higher limit of the magnetic field is close to materiallimit and significant increase of the value can not expected. And so,proposed is a method of recording on the recording medium while coerciveforce becomes small during the temporary magnetic softening of therecording medium caused by locally heating, stopping locally heating andnaturally cooling the recording medium, where the method ensures astability of the magnetic bit. This method is called thermally assistedmagnetic recording system.

In the thermally assisted magnetic recording system, it is preferable toheat the recording medium instantaneously. And the mechanism to heat therecording medium is not allowed to contact with the recording medium.Accordingly, it is usual to heat the recording medium utilizingabsorption of light and the system utilizing absorption of light iscalled optically assisted system. In a case of ultrahigh-densityrecording by optically assisted recording system, a necessary size of anoptical spot is about 20 nm. But ordinal optical system cannot condensethe optical spot to such extent due to diffraction limit.

Therefore, near field optical head, which uses near field light that isgenerated from an optical aperture of a size smaller than a wavelengthof an incident light. But the existing near field optical head has aproblem to be solved, which is low optical efficiency. There are somemethods to solve such problem.

For example, U.S. Pat. No. 6,795,380 discloses an optically-assistedmagnetic recording head to record information magnetically on a mediumcomprising: a pair of magnetic yokes having a gap therebetween,irradiation of light onto the gap generating an evanescent light; and amagnetic field generator applying a magneto-motive force to the magneticyokes to build a recording magnetic field across the gap, theinformation being recorded by the recording magnetic field on the mediumwhich is heated by irradiation of the evanescent light thereto.

Japanese unexamined patent application publication No. 2003-6913discloses a near field optical head including: a slider formed on asubstrate and an optical aperture of a size less than a wavelength of anincident light, the optical aperture is formed on the substrate, whereinthe near field optical head records and/or reproduces information byfloating from a surface of a recording medium with a predetermineddistance, wherein the floating power is generated by mutual movementbetween the slider and the surface of the recording medium, and havinginteraction with the surface of the recording medium via a near fieldlight generated from the optical aperture, and wherein the near fieldoptical head includes cyclic convex concave structure formed of metal,the structure is arranged around the optical aperture on the substrateand the optical aperture is arrange within the plane defined by a baseend face of the slider, and convex portion of the convex concavestructure is arranged on a light incident side with respect to the planedefined by the base end face of the slider.

And United States patent publication Number 2006/0045419 A1 discloses anoptical fiber coupling part capable of reducing coupling loss whilemaintaining a large operating distance, and having a good moduleassembling property. At least one GRIN lens having numerical aperture NAthat is larger than numerical aperture NAs of a light-emitting source(such as a semiconductor laser) is fusion-spliced with one end of theoptical fiber. The optical fiber coupling part can exit light fluxintroduced in the optical fiber as condensed light while maintaining alarge operating distance by utilizing a GRIN lens that is fusion-splicedwith the optical fiber having a large numerical aperture and loss of thelight can thereby be reduced.

But for the optically assisted magnetic recording head disclosed in U.S.Pat. No. 6,795,380, there is a description about irradiating light onthe gap generating near field light. The description is that the slideris carved with a groove on its top, in which an optical fiber isembedded, and the light beam emitted from the optical fiber is reflectedby the prism, and after passing through the transparent dielectricblock, it is irradiated to form a light spot near the gap of therecording element. Accordingly, there is no description about that thelight emitted from one end of the optical fiber diffuses in a spacebetween the one end of the optical fiber and the gap generating theevanescent light. Therefore it is easy to predict low optical efficiencyof the light emitted from the one end of the optical fiber.

In the near field optical head disclosed in Japanese unexamined patentapplication publication No. 2003-6913, a light emitted from the opticalfiber is reflected by a mirror surface and the reflected light iscondensed by a micro lens and irradiated on a near field lightgenerator. In this case, there is large loss of light at a deflectionsurface of the mirror and an incident surface of the micro lens.Therefore it is considered that optical efficiency of the light emittedfrom the one end of the optical fiber is not good. And it is difficultto make the near field optical head thin because the optical axis of themicro lens coincides with the direction in which the slider floats.

In the optical coupling part disclosed in United States patentpublication Number 2006/0045419 A1, it is possible to condense the lightflux introduced in the optical fiber to an optical spot of a size, forexample the same size as the size of light emitting point of lightemitting source LD (Laser Diode), with a GRIN lens having largenumerical aperture. There is a description that the operating distance(a distance from light emitting edge face to the optical spot) is set to30 μm, in this case, to obtain high coupling efficiency. In the case ofutilizing the optical coupling part for an optical head, an optical pathdeflecting means such as a prism will be required when trying to deflectthe light emitting from the optical fiber, for example about 90 degree,with respect to a light emitting direction. The optical length of theoptical path deflecting means is required to be equal or less than avalue that is given by multiplying the refractive index of the materialcomprising the prism by said 30 μm. It is difficult to structure suchoptical path deflecting means.

With a development of a high density information recording in aninformation-recording device such as HDD (Hard Disk Drive) in recentyears, miniaturization of a recording/reproducing head andminiaturization of a slider which configures the head are desired. Thesize of the slider is standardized as IDEMA (International Disk DriveEquipment and Materials Association) standard. In descending order,sliders are named as Mini slider, Micro slider, Nano slider, Pico sliderand Femto slider. In theses sliders, Nano slider, Pico slider and Femtoslider have gotten attention recently from a viewpoint of a size. Sizesand masses of theses sliders are indicated on Table 1.

TABLE 1 Size (length × width × thichness Mass Name of Slider (mm)) (mg)Nano slider 2.05 × 1.60 × 0.43 5.5 Pico slider 1.25 × 1.00 × 0.30 1.5Femto slider 0.85 × 0.70 × 0.23 0.5

Further, in high density information recording, as understandable fromthe size of sliders indicated in Table 1, it is necessary not only tomake the information density on one disc high, but also to providespatially high density slider by placing discs multilayered or bystoring in a small box. For example, when assuming the case of placingdiscs multilayered, distances between each discs are required to beminimum and thickness of the optical head including the thickness of theslider indicated in Table 1 is expected to be 1.5 mm or less.

SUMMARY OF THE INVENTION

This invention was conceived in view of the above problems and theobject thereof is to provide an optical head with good luminous efficacyand low height, and an optical recording apparatus that uses thisoptical head.

The foregoing problems are solved by the following construction.

An optical head comprising: a graded index lens which receives incidentlight radiated from a linear optical guide at one end surface of thegraded index lens and transmits the incident light from the other endsurface of the graded index lens, the graded index lens is adapted toform a light spot at a position that is away from the other end surfacefrom which the incident light is transmitted; a light path deflectionsection which deflects light transmitted from the graded index lens, thelight path deflection section is arranged between the other end surfacefrom which the incident light is transmitted and the position where thelight spot is formed; and a slider which floats on a recording mediumwhile moving relative to the recording medium, wherein at least thegraded index lens and the light path deflection section are installed onthe slider.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of the optical recording apparatus.

FIG. 2 is a cross-sectional view showing an example of the assist typemagnetic recording head including a magnetic recording element in theoptical head.

FIGS. 3(A) and 3(B) show examples of a bench.

FIGS. 4(A), 4(B) and 4(C) show an example of an optical waveguide.

FIGS. 5(A), 5(B) and 5(C) show examples of a plasmon probe.

FIG. 6 is a cross-sectional view showing an example of the structure ofan optical head.

FIG. 7 is a cross-sectional view showing an example of the structure ofan optical head.

FIG. 8 is a cross-sectional view showing an example of the structure ofan optical head.

FIG. 9 is a cross-sectional view showing an example of the structure ofan optical head.

FIG. 10 is a cross-sectional view showing an example of the structure ofan optical head.

FIG. 11 is a cross-sectional view showing an example of the structure ofan optical head.

FIG. 12(A) is a cross-sectional view showing an example of the structureof an optical head and FIG. 12(B) is a perspective view showing a prismportion.

FIG. 13(A) is a cross-sectional view showing an example of the structureof an optical head and FIG. 13(B) is a perspective view showing a prismportion.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a description with reference to drawings, of anoptically assisted type magnetic recording head which includes amagnetic recording element in the optical head of this invention and theoptical recording device comprising this optically assisted typemagnetic recording head. It is to be noted that for each of theembodiments the same parts have been assigned the same reference numbersand repeated descriptions thereof have been omitted.

FIG. 1 shows an example of the schematic structure of the opticalreading device (example, hard disk device) in which an opticallyassisted type magnetic recording head is loaded. The optical recordingapparatus 1A comprises in a case, a recording disk (magnetic recordingmedium) 2; a suspension 4 that is provided so as to be rotatable in thedirection of arrow A (tracking direction) with support shaft 5 as asupport point; a tracking actuator 6 that is mounted on the suspension4; an optically assisted type magnetic recording head (called opticalhead hereinafter) 3 that is mounted on the front end of the suspension4; and a motor (not shown) for rotating the disk 2 in the arrow Bdirection, a control section 7 to control the tracking actuator 6, themotor and recording, and the optical head 3 can move relative to thedisk 2 while floating thereon.

FIG. 2 shows an example of the optical head 3. The optical head 3 is anoptical head which utilizes light in recording information on the disk 2and comprises an optical system comprising an optical fiber 11 which isthe linear optical guiding element for guiding the light to the opticalhead 3; an optical assist section (optical waveguide) 16 for performingspot heating using near infrared light on the portion for recording ofthe disk 2; graded index lens 12 and 13 which guide the near infraredlaser light output from the optical fiber 11 to the optical assistsection 16; and a prism 14 which is a light path deflection section; amagnetic recording section 17 which performs writing of magneticinformation in the portion for recording of the disk 2; and a magneticreproduction section 18 for reading the magnetic information recorded onthe disk 2.

It is to be noted that in FIG. 2, the magnetic reproduction section 18,the optical waveguide 16 and the magnetic recording section 17 aresequentially arranged from the approach side to the exit side of therecording region of the disk 2 (→ direction in the drawing), but thearrangement sequence is not limited thereto. The magnetic recordingsection 17 may be positioned immediately after the exit side of theoptical waveguide 16, and thus the order may be optical waveguide 16,magnetic recording section 17, then magnetic reproduction section 18.

The light that is guided by the optical fiber 11 may, for example, belight that is output by a semiconductor laser, and the wavelength ofthis light is preferably the near infrared wavelength of 1.2 μm or more.(Near infrared wavelength is about 0.8 μm-2 μm and specific examples ofthe wavelength of the laser light are 1310 nm and 1550 nm). The nearinfrared laser light that was output from the end surface of the opticalfiber 11 is focused on the surface of the optical waveguide 16 that ison the slider 15 using the optical system (the graded index lens 12 and13 and the prism 14), and passes through the optical waveguide 16 whichforms the optical assist section, and is output from the optical head 3to the disk 2.

The slider 15 moves relative to the magnetic recording medium whilesliding above it, but foreign matter that attaches to the medium, ordefects of the medium, makes contact possible. In order to reduce thewear occurring at this time, it is preferable that an anti-wear materialwith a high degree of hardness is used for the material of the slider.For example, a ceramic material including Al₂O₃ such as AlTiC orzirconium TiN or the like may be used. A surface processing forincreasing anti-wear properties on the disk 2 side of the slider 15 maybe performed as anti-wear processing. For example if a DLC (diamond likecarbon) coating is used, the near infra-red transmittance is high andhardness of Hv=30 which is second only to diamond can be obtained.

In addition, the surface facing the disk 2 of the slider 15 may have asurface called an air bearing surface (ABS) for improving floating.

When the near infrared laser light output from the optical head 3 isradiated into the disk 2 as a tiny spot, the temperature of the portionof the disk 2 that is irradiated temporarily increases and the holdingpower of the disk 2 reduces. Magnetic information is written on theirradiated portion with reduced holding power by the magnetic recordingsection 17. The optical system for the optical head 3 will be describedin the following.

First the graded index lens 12 and 13 will be described. The gradedindex lens (called GRIN lens hereinafter) are cylindrical lens which usemedia with different refractive indexes (refractive index is larger asthe center is approached), and the lens are operated by continuouslychanging the refractive index. A specific examples of GRIN lens isSiGRIN (registered trademark) (silica GRIN, Toyo Glass Co., Ltd). Theradial direction graded index n(r) is shown by formula (1)

n(r)=N0+NR2×R ²  (1), where:

n(r): refractive index at position of distance r from the center; N0:refractive index at center portion; NR2: Constant showing the focusingpower of the GRIN lens.

One feature of the GRIN lens is that aligning the optical axis is easybecause it has graded index in the radial direction. For this reason,the optical axis of the optical fiber 11 and the GRIN lens 12 and 13 canbe easily aligned. In addition, in the case where the optical fiber isformed from quartz, because the material forming the GRIN lens 12 andthe GRIN lens 13 is the same as that of the optical fiber, they can beintegrally formed by melting to join them. This joining causes handlingto be easy, and at the same time, light loss is suppressed at thesurface where the optical fiber 11 and the GRIN lens 12 and the GRINlens 13 respectively connect and the light guided by the optical fibercan be effectively output by the GRIN lens 13.

The GRIN lens 12 and the GRIN lens 13 which are the graded index lenshave structure in which the light guided by the optical fiber 11 isfocused at a position away from the light output surface of the GRINlens 13 to form a light spot. The NA of the GRIN lens 12 and the GRINlens 13 are different and by selecting one of, or combining the GRINlens 12 and the GRIN lens 13, and by appropriately determining therespective lengths, the length of the graded index lens and the distancefrom the light output surface of the graded index lens to the light spotposition can be determined.

The distance from the end surface where light is output on the gradedindex lens to the position where the light spot is formed preferablysatisfies the conditional equation below.

0.5×d×n<s<n×b+n×(b ² +f ²)^(1/2)  (2)

where d: diameter of the graded index lens; s: length of the light pathfrom the end surface where light is output on the graded index lens tothe position where the light spot is formed; b: length of the slider inthe direction where the graded index lens and the light deflectionsection are aligned; n: refractive index of the medium in the light pathfrom the end surface where light is output on the graded index lens tothe position where the light spot is formed; f: the maximum permissibleheight in the direction in which the slider floats from the positionwhere the light spot is formed to the position where the light from thegraded index lens provided on the slider is output.

The conditional equation (2) defines the permissible range from the endsurface on the graded index lens where light is output to the positionwhere the light spot is formed, given that at least graded index lensand a first light path deflection section are provided on the sliderhaving the length b and a light spot can be formed on the upper surfaceor lower surface of the slider.

If the lower limit of conditional equation (2) is exceeded, a light pathdeflecting section such as a prism which deflects the light path cannotbe used. In addition if the upper limit of the conditional equation (2)is exceeded, it becomes impossible to form a light spot at a prescribedposition which is on the upper surface or the lower surface of theslider with one of the light deflection section such as the graded indexlens which focus light flux on the upper surface of the slider having alength b.

The length of the slider shown in the conditional equation (2) can beused for the size (length) of the nano slider, the pico slider, and thefemto slider shown in Table 1. The height f may be suitably determinedby the height of the optical head and may, for example, be about 1 mm.

The diameter of GRIN lens 12 and GRIN lens 13 which are the graded indexlens and the diameter of the optical fiber 11 are preferablysubstantially the same ±10%, and they are even more preferably the same.Because the optical fiber 11, the GRIN lens 12 and the GRIN lens 13 canbe joined by melting as described above, if they all have substantiallythe same diameter, it is easy to align the centers and perform thejoining operation. In addition, in the case where the optical fiber 11,the GRIN lens 12 and the GRIN lens 13 that are joined on the slider 15(simply called joined optical elements hereinafter) are provided at aprescribed position, the height and direction of the joined opticalelements can be set with high accuracy and fixed with an adhesive or thelike by causing the configuration to have a simple V groove (see FIGS.3(A) and 3(B)) on the slider 15. Furthermore, if the diameter of theGRIN lens 12 and the GRIN lens 13 are the same as the diameter of theoptical fiber, the optical head can be made thinner as a matter ofcourse.

In the case where the graded index lens and the optical fiber areprovided on the slider 15, a V-groove or a member including a V-grooveis prepared (called bench hereinafter) and after the graded index lensand the optical fiber are fixed in this bench, it may be fixed on theslider 15 and the bench structure may also be formed directly on theopposite surface to the surface facing the magnetic recording surface ofthe slider 15.

An example of the bench is shown in FIGS. 3(A) and 3(B). FIG. 3(A) showsthe bench on which a V-groove 15 a is provided directly on the uppersurface of the slider 15. 15 b shows the surface for fixing the prism.The V-groove 15 a of FIG. 3 (A) may be formed as a separate member whichis a bench. Also, FIG. 3 (B) shows a bench which is formed as a separatemember from the slider and in which V-groove 15 c and the prism 15 d areintegrally formed.

Of course, the bench and the slider may be integrally formed. Also,other examples in which the V-groove and the prism are integral areshown in prism 74 of FIGS. 12(A) and 12(B) and prism 84 of FIGS. 13(A)and 13(B) (see working examples 7 and 8).

When the V-groove and the prism are integral, the positionalrelationship between the prism and the joined optical elements can besimple, and the optical head can be assembled accurately and simply. Itis to be noted that in FIG. 2 and FIG. 6 to FIG. 11, the bench portionis not shown.

Also, by providing the V-groove, the height of the graded index lens andthe optical axis direction can be stipulated and movement in the opticalaxis direction can be done easily, and for example, assembly by pressingthe light output surface of the GRIN lens which has a flat end surfaceto the light incident surface of the prism can be easily done. In thismanner, by bringing the light incident surface of the prism and thelight output surface of the GRIN lens into close contact such that airis not caught between the surfaces, the light that is output from theoptical fiber 11 can be input into the prism through the GRIN lens thatare joined by the melting without passing through an air layer and thusan optical head with good luminous efficacy can be formed.

It is preferable that the prism 14, which is the light path deflectionsection for deflecting the light path between the light output surfaceof the GRIN lens 13 and the position of the light spot by 90°, isprovided. By providing the prism 14, the advance direction of the lightthat is output from the optical fiber 11 that is parallel to themagnetic recording surface and converged by the GRIN lens 12 and theGRIN lens 13 which are the graded index lens can be made orthogonal tomagnetic recording surface.

The height of the prism 14 is larger than the radius of the graded indexlens which is optically joined with the prism, such as GRIN lens 13, andpreferably less than substantially the same diameter thereof. By formingthe prism 14 to have this height, the light path can be deflectedwithout increasing loss of light output from the graded index lens whilesuppressing the height of the optical head.

In addition, the light path deflection section can be a mirror that hasa light deflecting surface, but it is preferably a prism that canutilize total reflection in view of reflection efficiency. If thedeflection surface is a mirror, the reflection efficiency is about 80%,while if a prism that utilizes total reflection is used, it can be closeto 100%. Furthermore, in the case where total reflection is used, therefraction index for forming the prism is preferably large. When therefraction index is large, the angle of incidence formed by totalreflection can be made smaller. That is to say, if, for example, theoptical axis of the converging light flux is made incident on thedeflection surface at an angle of incidence of 45°, the light flux ismade incident with some width for the angle of incidence, but the amountof reflected light for light from the side where the angle of incidenceis small can be increased.

The position for forming the spotlight using the graded index lenscomprising the GRIN lens 12 and 13 is on the upper surface of theslider, and an optical waveguide is preferably provided directlytherebeneath. By providing the optical waveguide, the light spot thatconverges on the upper surface of the slider can be efficiently guidedto the lower surface of the slider without loss of the spot diameter.The direction of the light that converges in the optical waveguide ispreferably substantially orthogonal with respect to the input surfacefor the optical waveguide. The guiding efficiency on the opticalwaveguide decreases with incline from the orthogonal direction, and whenthere is an incline of about 30°, little or no guiding is done, and thusby causing the direction to be substantially orthogonal ±10° C., lightcan be efficiently guided. For example, in the case where the opticalwaveguide is provided so as to incline with respect to the surface wherethe slider moves relatively, it is more preferable that the lightincident end surface of the optical waveguide is formed as a surfacethat is orthogonal to the incoming light than as a surface that isparallel to the direction of movement of the slider, in view of luminousefficacy.

In addition, particularly in the case where the optical waveguide isprovided orthogonal to the direction of relative movement of the slider,the converging light which has an angle for the light to converge doesnot need to pass inside the slider and thus the magnetic recordingsection and magnetic reproduction section can be easily provided at aposition near the vicinity of the optical waveguide in the directionwhere the magnetic recording surface moves relatively. Thus an efficientoptically assisted type optical head can be formed.

In addition, if the optical waveguide includes a light spot sizeconversion function which is described hereinafter, the diameter of thelight spot formed on the input surface of the optical waveguide can bereduced at the output surface with respect to the diameter at the inputsurface of the optical waveguide. As a result, a smaller light spotdiameter can be formed on the recording medium surface and this issuitable for high recording density.

An example of the optical waveguide including a light spot sizeconversion function is shown in FIGS. 4(A), 4(B) and 4(C). FIGS. 4(A)and 4(B) show the portion of the optical waveguide viewed from thedirection in which the optical head moves relatively, while FIG. 4(C)the view from orthogonal direction with respect to the direction ofmovement and the parallel direction with respect to the magneticrecording surface. The optical waveguide shown in FIGS. 4(A), 4(B) and4(C) is formed of a core 16 a (example Si), a sub-core 16 b (exampleSiON) and a clad 16 c (example SiO₂). As shown in FIG. 4(C), there is aplasmon probe 16 f for near field light emission at the light outputposition of the optical waveguide or the vicinity thereof. A specificexamples of the plasmon probe 16 f are shown in FIGS. 5(A), (B) and (C).

FIG. 5(A) shows a plasmon probe 16 f formed from a flat triangular thinmetal film (material: aluminum, gold, silver or the like for example)and FIG. 5 (B) shows a plasmon probe 16 f formed from a powder type flatthin metal film) (material: aluminum, gold, silver or the like forexample) and each of them includes an antenna which has a peak which isless than the curve radius of 20 nm. FIG. 5 (C) shows also a plasmonprobe 16 f formed from a flat thin metal film (material: aluminum, gold,silver or the like for example) which has openings, and includes anantenna which has a peak) which is less than the curve radius of 20 nm.When light acts on these plasmon probes 16 f, near field light isgenerated in the vicinity of the peak P, and recording or reproductionwhich uses light of an extremely small spot size can be performed. Thatis to say, by providing the plasmon probe 16 f at the light outputposition of the optical waveguide or in the vicinity thereof, if localplasmon is generated, the size of the light spot formed by the opticalwaveguide can be made smaller and can be used in high density recording.It is to be noted that the peak P of the plasmon probe 16 f ispreferably positioned in the center of the core 16 a.

The required spot diameter for performing super high density recordingusing the optically assisted type is approximately 20 nm, and when lightuse efficiency is considered, the mode field diameter (MFD) in theplasmon probe 16 f is preferable about 0.3 μm. With this MFD size, lightinput is difficult and thus it is necessary to perform spot sizeconversion to decrease the spot diameter from about 5 μm to a fewhundred nm. The example of the optical waveguide shown in FIGS. 4(A),4(B) and 4(C) has a structure in which spot conversion is performed inorder to facilitate light input.

In FIGS. 4(A), 4(B) and 4(C), as shown by the cross-section in FIG.4(C), the width of the core 16 a is constant from the light incidentside to the light output side, but in the cross-section in FIG. 4(A) itchanges so as to gradually widen from the input side to the output sidein the sub-core 16 b. The mode field diameter is changed due to smoothchanges in the optical waveguide. That is to say, as shown in FIG. 4(A)the width of the core 16 a of the optical waveguide is 0.1 μm or less atthe light incident side and 0.3 μm at the light output side, but asshown in FIG. 4(B), at the input side, an optical waveguide of about 5μm is formed by the sub-core 16 b and then the optical waveguide isgradually optically bonded to the core 16 a and the mode field diametercan be reduced. In this manner, given that the mode field diameter atthe optical output side of the optical waveguide is dm and the modefield diameter at the optical input side of the optical waveguide is Dm,it is preferable that the mode field diameter is converted by smoothlychanging the optical waveguide diameter such that Dm>dm is satisfied.

In addition, the optical head comprising an optical waveguide isdescribed above, but in the optical systems shown in FIGS. 8 and 9 (SeeWorking Examples 3 and 4 for details), the structure is such that thelight that is guided by the optical fiber 11 focuses on the lowersurface of the sliders 35 and 45 which float and run on the disk 2, andlight is output from the optical heads 30 and 40 towards the disk (notshown). By having this kind of structure, an element for focusing lightis not provided between the optical system and the slider, and thus theoptical head can be formed thinner. In addition, because there is nooptical waveguide, the structure of the sliders 35 and 45 is simple andthe optical heads 30 and 40 can be formed easily. The conditionalequation (2) can also be used for this structure.

The optical head described up to this point is an optically assistedtype magnetic recording head which uses light for recording informationon the disk 2, but an optical head which uses light for recordinginformation on a recording medium and does not include magneticreproduction section 17 and magnetic recording section 18 such as anoptical head which performs near field or phase change recording or maybe used and the plasmon probe 16 f described above may be arranged atthe light output position of the optical waveguide 16 or in the vicinitythereof.

WORKING EXAMPLES

The following is a description of the working examples of thisinvention.

The common conditions in Working Examples 1 to 9 below are shown in thefollowing. Equation (1) for the refraction index of the GRIN lens usingwavelength 1.31 μm is shown again below.

n(r)=NO+NR2×r ²  (1),

where r is the distance from the center (distance in the diametricaldirection from the center).

The constants required for showing the refraction index of GRIN lens Aand GRIN lens B which are the graded index lens used in Working Examples1 to 9 below Equation (1) above are shown below.

GRIN lens A (NA: 0.166)

N0=1.479606

NR2=−2.380952

GRIN lens B (NA: 0.395)

N0=1.540737

NR2=−12.47619

Diameter of GRIN A and GRIN B: 125 μm (in examples 1-8)

Diameter of GRIN A and GRIN B: 80 μm (in example 9)

In the examples below, the magnetic recording section, the magneticreproduction section and the plasma probe are not included, but in thecase of the optically assisted type magnetic recording head, or in thecase where super high density recording is performed, these may, as amatter of course, be provided.

In the figures corresponding to Working Examples 1 to 6 and Example 9respectively, the bench for fixing the joined optical elements in whichthe optical fiber, the GRIN lens A, GRIN lens B is not shown, but thereis a bench comprising a V-groove on the surface of the slider.

The joining surface and the last end surface on the optical paths ofFIG. 6-FIGS. 13(A) and 13(B) are assigned numbers from f0 to f1, f2,etc. These correspond respectively to light sources 1, 2 of the surfacesshown in the table corresponding to the figures describing the workingexamples below.

Working Example 1

10 in FIG. 6 is the optical head, 11 is the optical fiber, 12 is theGRIN lens A, 13 is GRIN lens B, 14 is the prism, 15 is the slider and 16is the optical waveguide.

In FIG. 6, GRIN lens A12, GRIN lens B13 and prism 14 are installed onthe slider 15 formed of AlTiC of length of the pico slider (in themovement direction) of 1.25 mm, thickness (floating direction) of 0.3mm, and depth of 1 mm. The light flux output from the optical fiber 11with diameter 125 μm forms a parallel light flux using the GRIN lens A12which have a length of 0.875 mm, and passes through the GRIN lens B13with a length of 0.15 mm, and the parallel light enters as converginglight into the prism 14 which is formed of quartz and whose deflectionsurface is 45°. The light flux that was deflected at approximately 90°by the prism 14 forms a light spot that is focused so as to besubstantially orthogonal on the input end surface of the opticalwaveguide 16, and is thereby optically bonded. Three elements which arethe optical fiber 11, the GRIN lens A12 and the GRIN lens B13 are joinedby melting, and positioning can be performed as one unit, and the endsurface of the GRIN lens B13 is pressed onto the light incident surfaceof the prism 14 and fixed by adhesion such that an air layer is notsandwiched between the surfaces. The mode field diameter of the opticalfiber 11 is approximately 10 μm and the mode field diameter of theoptical waveguide 16 is also approximately 10 μm. By combining the GRINlens A12 and the GRIN lens B13, the light output from the optical fiber11 can form light spots which correspond to the mode field diameter ofthe optical waveguide 16, and the magnification of the optical systemcan be 1:1.

The values of the GRIN lens 12 and 13 and the prism 14 are shown inTable 2 below.

TABLE 2 Distance between Curve axis and upper Surface radius surface(mm) Refraction index (Light source) ∞ 0 — 1 ∞ 0.875 See GRIN Lens A 2 ∞0.15 See GRIN Lens B 3 ∞ 0.3376553 1.479606 4 ∞ — —

Working Example 2

20 in FIG. 7 is the optical head, 11 is the optical fiber, 12 is theGRIN lens A, 13 is GRIN lens B, 24 is the prism, 15 is the slider and 16is the optical waveguide.

In FIG. 7, the GRIN lens A12, GRIN lens B13 and the prism 24 areinstalled on the slider 15. The light output from the optical fiber 11passes through the GRIN lens A12, GRIN lens B13 and enters as converginglight into the prism 24 which is formed of SF6 glass and whosedeflection surface is 45°. The light flux that was deflected atapproximately 90° by the prism 24 forms a light spot that is focused soas to be substantially orthogonal to the input end surface of theoptical waveguide 16, and is optically bonded. Three elements which arethe optical fiber 11, the GRIN lens A12 and the GRIN lens B13 are joinedby melting, and positioning can be performed as one unit, and the endsurface of the GRIN lens B13 is pressed onto the light incident surfaceof the prism 24 and fixed by adhesion such that an air layer is notsandwiched between the surfaces. The mode field diameter of the opticalfiber 11 is approximately 10 μm and the mode field diameter of theoptical waveguide 16 is also approximately 10 μm. By combining the GRINlens A12 and the GRIN lens B13, the light output from the optical fiber11 can form light spots which correspond to the mode field diameter ofthe optical waveguide 16, and the magnification of the optical systemcan be 1:1.

Because the material or forming prism 24 is SF6 glass which has a largerrefractive index than quartz in Working Example 1 above, reflectance dueto total reflection on the deflection surface can be increased andluminous efficacy thereby increased.

The values for the GRIN lenses 12 and 13 and the prism 24 are shown inTable 3 below.

TABLE 3 Distance between Curve axis and upper Surface radius surface(mm) Refraction index (Light source) ∞ 0 — 1 ∞ 0.875 See GRIN Lens A 2 ∞0.15 See GRIN Lens B 3 ∞ 0.4128449 1.76812808 4 ∞ — —

Working Example 3

30 in FIG. 8 is the optical head, 11 is the optical fiber, 12 is theGRIN lens A, 13 is GRIN lens B, 34 is the prism and 35 is the slider.

In FIG. 8, optical fiber 11, GRIN lens A12, GRIN lens B13 and prism 34are installed on the slider 35 formed from SF6 through which light froman optical fiber of length 1.25 mm, thickness 0.3 mm, and depth of 1 mmcan pass. The light output from the optical fiber 11 passes through theGRIN lens A12, GRIN lens B13 and enters as converging light, into theprism 34 which is formed of SF6 glass and whose deflection surface is45°. The light flux that was deflected at approximately 90° by the prism34 can form a light spot that is focused on the lower surface of theslider 35. Because the slider 35 does not have an optical waveguide, thestructure of the slider 35 can be simple. Three elements which are theoptical fiber 11, the GRIN lens 12 and the GRIN lens 13 are joined bymelting, and positioning can be performed as one unit, and the endsurface of the GRIN lens B13 is pressed onto the light incident surfaceof the prism 34 and fixed by adhesion such that an air layer is notsandwiched between the surfaces. The mode field diameter of the opticalfiber 11 is approximately 10 μm and because the size of the focus spoton the lower surface of slider 35 is also 10 μm, the magnification ofthe optical system is 1:1.

The values for the GRIN lenses 12 and 13 and the prism 34 are the sameas in Table 3 above.

Working Example 4

40 in FIG. 9 is the optical head, 11 is the optical fiber, 12 is theGRIN lens A, 13 is GRIN lens B, and 45 the slider which is integral withthe prism.

As is the case in Working Example 3, because the slider 35 does not havean optical waveguide, the structure of the slider 35 can be simple.Furthermore because the prism and the slider are integrally formed, thestructure is such that assembly is easy.

The values for the GRIN lenses 12 and 13 and the prism and slider 45 arethe same as in Table 3 above.

50 in FIG. 10 is the optical head, 11 is the optical fiber, 52 is theGRIN lens B, 54 is the prism, 15 is the slider and 16 is the opticalwaveguide.

In FIG. 10, the optical fiber 11, GRIN lens B52 and the prism 54 areinstalled on the slider 15. The light output from the optical fiber 11passes through the GRIN lens B52 having a length of 0.565 mm and entersas converging light into the prism 54 which is formed of SF6 glass ofheight 0.125 mm, length 0.336 mm and depth 0.125 mm and whose deflectionsurface is 45°. By forming the graded index lens as one of the GRIN lensB52, the structure can be made simple. The light flux that was deflectedat approximately 90° by the prism 54 forms a light spot that is focusedso as to be substantially orthogonal to the input end surface of theoptical waveguide 16, and is optically bonded. The optical fiber 11, andthe GRIN lens 52 are joined by melting, and positioning can be performedas one unit, and the end surface of the GRIN lens B52 is pressed ontothe light incident surface of the prism 54 and fixed by adhesion suchthat an air layer is not sandwiched between the surfaces. The lightoutput from the optical fiber 11 having a mode field diameter ofapproximately 10 μm suppresses the length of GRIN lens B52 by having oneGRIN lens B52 and the length of the prism 54 can be ensured. Because thelength of the GRIN lens B52 is suppressed, the converged state of thelight has a small structure with small NA. As a result, the size of thelight spot is approximately 20 μm and the magnification of the opticalsystem can be 2:1.

The values for the GRIN lens B52 the prism 54 are shown in Table 4below.

TABLE 4 Distance between Curve axis and upper Surface radius surface(mm) Refraction index (Light source) ∞ 0 — 1 ∞ 0.564685 See GRIN Lens B2 ∞ 0.3367499 1.76812808 3 ∞ — —

Working Example 6

60 in FIG. 11 is the optical head, 11 is the optical fiber, 62 is theGRIN lens B, 64 is the prism, 15 is the slider and 16 is the opticalwaveguide.

In FIG. 11, the optical fiber 11, GRIN lens B62 and the prism 64 areinstalled on the slider 15. The light flux from the optical fiber 11passes through the GRIN lens B62 having a length of approximately 0.678mm and enters as converging light into the prism 64 which is formed ofSF6 glass of height 0.125 mm, length 0.125 mm and depth 0.125 mm andwhose deflection surface is 45°. By forming the graded index lens as oneof the GRIN lens B62, the structure is simplified. The light flux thatwas deflected at approximately 90° by the prism 64 forms a light spotthat is focused so as to be substantially orthogonal to the input endsurface of the optical waveguide 16, and is optically bonded. Theoptical fiber 11 and the GRIN lens B62 are joined by melting, andpositioning can be performed as one unit, and the end surface of theGRIN lens B62 is pressed onto the light incident surface of the prism 64and fixed by adhesion such that an air layer is not sandwiched betweenthe surfaces. The light output from the optical fiber 11 having a modefield diameter of approximately 10 μm has a larger converged state andlarger NA as a result of having one GRIN lens B62 and making the lengthof GRIN lens B62 long compared to that of Working Example 5. As aresult, the size of the optical spot is approximately 14 μm and themagnification of the optical system can be 1:4:1.

The specifications for the GRIN lens B62 and the prism 64 are shown inTable 5 below.

TABLE 5 Distance between Curve axis and upper Surface radius surface(mm) Refraction index (Light source) ∞ 0 — 1 ∞ 0.6776729 See GRIN Lens B2 ∞ 0.125 1.76812808 3 ∞ — —

Working Example 7

70 in FIG. 12(A) is the optical head, 11 is the optical fiber, 12 is theGRIN lens A, 13 is the GRIN lens B, 74 is the prism that is formedintegrally with the V-groove, 15 is the slider and 16 is the opticalwaveguide. FIG. 12(B) is a perspective view of the prism 74 that isintegrally formed with the V-groove.

In FIG. 12 (A), the prism 74 that is integrally formed with the V-grooveis installed on the slider 15. Three elements which are the opticalfiber 11, the GRIN lens A12 and the GRIN lens B13 are joined by meltingwith the V groove of the prism 74 that is integral with the V-groove toform one unit, and the end surface of the GRIN lens B13 is pressed ontothe light incident surface of the prism 74 and fixed by adhesion suchthat an air layer is not sandwiched between the surfaces.

The light flux from the optical fiber 11 passes through the GRIN lensA12 and the GRIN lens B13 and enters as converging light into the prism74 that is integral with the V-groove and made of polycarbonate andwhose deflection surface is 45°. The light flux that was deflected atapproximately 90° by the prism 74 that is integral with the V-grooveforms a light spot that is focused so as to be substantially orthogonalto the input end surface of the optical waveguide 16, and is opticallybonded.

The mode field diameter of the optical fiber 11 is approximately 10 μmand the mode field diameter of the optical waveguide 16 is alsoapproximately 10 μm. By combining the GRIN lens A12 and the GRIN lensB13, the light output from the optical fiber 11 can form light spotswhich correspond to the mode field diameter of the optical waveguide 16,and the magnification of the optical system can be 1:1.

The values for the GRIN lenses 12 and the 13 and the prism 74 are shownin Table 6 below.

TABLE 6 Distance between Curve axis and upper Surface radius surface(mm) Refraction index (Light source) ∞ 0 — 1 ∞ 0.875 See GRIN Lens A 2 ∞0.125 See GRIN Lens B 3 ∞ 0.364518 1.559211 4 ∞ — —

Working Example 8

80 in FIG. 13(A) is the optical head, 11 is the optical fiber, 12 is theGRIN lens A, 13 is the GRIN lens B, 84 is the prism that is integralwith the V-groove and inclines at 10°, 15 is the slider and 16 is theoptical waveguide. FIG. 13(B) is a perspective view of the prism 84 thatis integral with the V-groove in FIG. 13(A).

In FIG. 13(A), the prism 84 that is integral with the V-groove isinstalled on the slider 15. Three elements which are the optical fiber11, the GRIN lens A12 and the GRIN lens B13 are joined by melting withthe V-groove of the prism 84 that is integral with the V-groove to formone unit, and the end surface of the GRIN lens B13 is pressed onto thelight incident surface of the prism 84 and fixed by adhesion such thatan air layer is not sandwiched between the surfaces.

The light flux from the optical fiber 11 passes, through the GRIN lensA12 and the GRIN lens B13 and enters as converging light into the prism84 that is integral with the V-groove and made of polycarbonate andwhose deflection surface is 50°. The light flux that was deflected atapproximately 100° by the prism 84 that is integral with the V-grooveforms a light spot that is focused so as to be substantially orthogonalto the input end surface of the optical waveguide 16, and is opticallybonded. Because the angle for deflection the light flux is 100°, thereflection state at the deflection surface of the prism made ofpolycarbonate which has a smaller refraction index than SF6, is a stateclose to total reflection, and furthermore, by inclining the V-groove at10°, because light is input in the orthogonal direction with respect tothe input surface of the optical waveguide 16, the luminous efficacy isbetter than that of Working Example 7. The mode field diameter of theoptical fiber 11 is approximately 10 μm and the mode field diameter ofthe optical waveguide 16 is also approximately 10 μm. By combining theGRIN lens A12 and the GRIN lens B13, the light output from the opticalfiber 11 can form light spots which correspond to the mode fielddiameter of the optical waveguide 16, and the magnification of theoptical system can be 1:1.

The values for the GRIN lenses 12 and the 13 and the prism 84 are thesame as those of Table 6 above.

Working Example 9

10 in FIG. 6 is the optical head, 11 is the optical fiber, 12 is theGRIN lens A, 13 is GRIN lens B, 14 is the prism, 15 is the slider and 16is the optical waveguide.

In FIG. 6, GRIN lens A12, GRIN lens B13 and prism 14 are installed onthe slider 15 formed of AlTiC of length of the pico slider (in themovement direction) of 1.25 mm, thickness (floating direction) of 0.3mm, and depth of 1 mm. The light flux output from the optical fiber 11with diameter 80 μm forms a parallel light flux using the GRIN lens A12which have a length of 0.875 mm, and passes through the GRIN lens B13with a length of 0.310792 mm, and the parallel light enters asconverging light into the prism 14 which is formed of quartz and whosedeflection surface is 45°. The light flux that was deflected atapproximately 90° by the prism 14 forms a light spot that is focused soas to be substantially orthogonal on the input end surface of theoptical waveguide 16, and is thereby optically bonded. Three elementswhich are the optical fiber 11, the GRIN lens A12 and the GRIN lens B13are joined by melting, and positioning can be performed as one unit, andthe end surface of the GRIN lens B13 is pressed onto the light incidentsurface of the prism 14 and fixed by adhesion such that an air layer isnot sandwiched between the surfaces. The mode field diameter of theoptical fiber 11 is approximately 3.3 μm and the mode field diameter ofthe optical waveguide 16 is also approximately 11.87 μm. By combiningthe GRIN lens A12 and the GRIN lens B13, the light output from theoptical fiber 11 can form light spots which correspond to the mode fielddiameter of the optical waveguide 16, and the magnification of theoptical system can be 1:0.57.

The values of the GRIN lens A 12, the GRIN lens B 13 and the prism 14are shown in Table 7 below.

TABLE 7 Distance between Curve axis and upper Surface radius surface(mm) Refraction index (Light source) ∞ 0 — 1 ∞ 0.875 See GRIN Lens A 2 ∞0.310792 See GRIN Lens B 3 ∞ 0.08 1.521414476 4 ∞ — —

(Suitability of Conditional Equation (2))

In Working Examples 1-9, the maximum permissible height f from theposition where the light spot is formed to the position where the lightfrom the graded index lens provided on the slider is 1 mm. Whether theconditional equation 2 is suitable or unsuitable is shown in Table 7. Asshown in Table 8, it is clear that it is suitable in all of WorkingExamples 1-9.

TABLE 8 Suitable/ Unsuitable for conditional 0.5 × d × n S n × (b +(b² + f²)^(1/2)) equation Working 0.092475 0.499597 4.216877 SuitableExample 1 Working 0.110508 0.729963 5.039165 Suitable Examples 2, 3, 4Working 0.092475 0.595417 5.039165 Suitable Example 5 Working 0.1105080.221016 5.039165 Suitable Example 6 Working 0.097451 0.568360 4.443751Suitable Examples 7, 8 Working 0.060857 0.121713 4.336031 SuitableExample 9

According to this invention, in a state where a linear optical guide anda graded index lens are arranged in a straight line, a light spot can beformed on a line extended therefrom and by including a light pathdeflection section, the light path can be deflected at 90°. As a result,a linear optical guide and graded index lens are provided parallel tothe recording medium surface and light in the orthogonal direction ofthe recording medium surface converges and the light spot is formed.Furthermore, a light incident end surface of a prism which is a linearoptical guide, a graded index lens, and a light path deflection sectionmay be formed in a density state where there is little light loss.

And, by changing combination of the GRIN lenses, it is possible toselect image formation magnification from enlargement, same size andreduction, freely. A lot of flexibility for the parts (optical fiber,optical waveguide) arranged at both side of the GRIN les is attained. Asa result of the flexibility, an optical head that is optically highefficient and being small height could be attained. To be more precise,generally when utilizing an optical waveguide, image formationmagnification becomes enlargement and then the size of the optical spotbecomes larger than the incident surface of the optical waveguide.Accordingly, connection efficiency at the incident side of the opticalwaveguide becomes extremely low. Further, when generating near fieldlight, efficiency of convergence to near field light becomes low. Byusing two GRIN lenses, it becomes possible to provide optically highefficient structure depending on the parts to be used.

Thus an optical head with good luminous efficacy and low height, and anoptical recording apparatus using this optical head is provided.

1. An optical head comprising: a graded index lens which receivesincident light radiated from a linear optical guide at one end surfaceof the graded index lens and transmits the incident light from the otherend surface of the graded index lens, the graded index lens is adaptedto form a light spot at a position that is away from the other endsurface from which the incident light is transmitted; a light pathdeflection section which deflects light transmitted from the gradedindex lens, the light path deflection section is arranged between theother end surface from which the incident light is transmitted and theposition where the light spot is formed; and a slider which floats on arecording medium while moving relative to the recording medium, whereinat least the graded index lens and the light path deflection section areinstalled on the slider.
 2. The optical head of claim 1, the gradedindex lens comprises a first index graded lens having a first refractiveindex profile and a second index graded lens having a second refractiveindex profile.
 3. The optical head of claim 1, the light path deflectionsection is a prism.
 4. The optical head of claim 1, an optical pathlength between the other end surface from which the incident light istransmitted and the position where the light spot is formed satisfiesfollowing conditional equation:0.5×d×n<s<n×(b+n×(b ² +f ²)^(1/2)) where d: diameter of the graded indexlens; s: an optical path length between the other end surface from whichthe incident light is transmitted and the position where the light spotis formed; b: length of the slider in a direction in which the gradedindex lens and the light deflection section are aligned; n: refractiveindex of a medium in the optical path between the other end surface fromwhich the incident light is transmitted and the position where the lightspot is formed; f: the maximum permissible height in the direction inwhich the slider floats from the position where the light spot is formedto the position where the light from the graded index lens provided onthe slider is output.
 5. The optical head of claim 1, wherein thediameter of the linear optical guide and the diameter of the gradedindex lens are substantially same.
 6. The optical head of claim 1,further comprising a bench to fix the index grade lens.
 7. The opticalhead of claim 6, the bench and the light path deflection section areintegrally formed.
 8. The optical head of claim 1, the light radiatedfrom the linear optical guide does not pass through an air layer untilthe light forms the light spot at the position.
 9. The optical head ofclaim 1, wherein the slider is provided with an optical waveguide thatincludes a light incident surface where the light spot is formed and theoptical waveguide guides the light spot incident on the light incidentsurface and radiates the light spot to the recording medium.
 10. Theoptical head of claim 9, further comprising a plasmon probe forgenerating near field light provided at a position where the light istransmitted from the optical waveguide or near the position.
 11. Theoptical head of claim 1, further comprising a plasmon probe forgenerating near field light at a position where the light is transmittedfrom the optical waveguide or near the position. the position where thelight spot is formed is a surface of the slider facing the recordingmedium.
 12. The optical head of claim 11, further comprising a plasmonprobe for generating near field light provided at a position where thelight spot is formed and transmitted or provided near the position. 13.The optical head of claim 1, further comprising magnetic recordingelement.
 14. An optical recording apparatus comprising: a recordingmedium; the optical head of claim 1; and a control section to controlthe recording medium and the optical head.